There exists a close-knit community of general aviation (GA) enthusiasts who build and fly “homebuilt” or “kit-built” aircraft. Like commercially built aircraft, these planes have “N-number” registrations issued by the Federal Aviation Administration (FAA), but do not undergo the same rigorous FAA airworthiness certification standards that are followed by such stalwart aircraft manufactures as Cessna and Piper.
Experimental Amateur-Built (EAB) aircraft represent a small, but growing percentage of active general aviation aircraft and manual flight hours. However, they account for a disproportionate share of fatal GA accidents. This year, the Safety Board has investigated more than 180 accidents involving homebuilt aircraft.
“Homebuilt airplanes are popular because they are significantly more affordable to pilots, especially due to fuel prices and inflation,” said Sandy Rowlett, Deputy Chief, Operational Factors Divison, Office of Aviation Safety. “Plus, they are a heck of a lot of fun to fly. At NTSB, we have about a half-a-dozen air safety investigators who have built and fly them.”
A recent review of NTSB aviation accident statistics revealed that from 2004 to 2008, approximately 18 percent of all fatal GA accidents involved EAB aircraft, even though those aircraft represented an average of only 8 percent of the entire GA fleet, and about 4 percent of the flight hours. The accident rate for EAB was 6.29 fatal accidents per 100,000 flight hours in contrast to an average of 1.09 for FAA-certified single-engine piston airplanes, and 1.19 for all of GA.
Last year, following several fatal accidents involving in-flight structural breakups of the Zodiac, a homebuilt aircraft, the Safety Board issued several recommendations to the FAA. These recommendations addressed: mitigating the potential for aerodynamic flutter, correcting airspeed correlations, and evaluating the sensitivity of flight controls.
Most EAB aircraft are assembled from kits that are sold by a kit manufacturer. The majority are fairly conventional-looking airplanes and are made of aluminum. However, since these aircraft are “experimental”, a builder/pilot can customize them by putting in an automobile engine for example or using components from other vehicles or applications. “Because of the less stringent rules that govern the design and construction of these types of aircraft, many feel that this category of aircraft encourages innovation and results in things like new material utilization, fuel efficiency, and advanced glass cockpits, to name a few,” Rowlett said.
However, if the “major" portion of the fabrication and assembly is undertaken and completed by persons solely for educational or recreational purposes, these aircraft are granted “experimental” airworthiness certificates by the FAA. Each aircraft is individually inspected by a local FAA airworthiness inspector or designated airworthiness inspector for construction quality. No FAA certification flight testing is performed, and the pilots who own these aircrafts must test these themselves. After a 40-hour period of restricted flying, passengers are allowed to be carried. However, these aircraft cannot be used for compensation or hire due to their experimental classification.
“Because there are no requirements that the aircraft meet any FAA certification standards, the strength and reliability of a particular design may be unknown,” Rowlett said. “The aircraft may also not be as aerodynamically stable and forgiving as FAA-certified aircraft such as those made by aircraft manufacturers."
This July, the NTSB participated in the 2010 Experimental Aircraft Association Annual convention, the largest gathering of sport aviation enthusiasts in the United States. The 55-year old event, known within the industry as AirVenture or Oshkosh, is held in Oshkosh, Wisconsin. The event is considered the Mecca of sport aviation enthusiasts, where about 10 percent of all registered GA airplanes in the country fly in to this small town just south of Green Bay to catch a good air show, view thousands of unique homebuilt aircraft, and consult with other pilots and builders.
During the five day gathering, NTSB aviation investigators presented the following sessions: (1)The NTSB Accident Investigation Process by Robert Benzon, (2) Aviation Accidents Involving Air Traffice Control Issues by Scott Dunham, (3) Air Traffic Control Specialist and (4) NTSB Safety Study on Glass Cockpits in General Aviation, Loren Groff, Safety Analyst. Additionally, like every year, NTSB investigators were present at the Board’s exhibition booth to discuss with attendees safety lessons learned from previous EAB accidents investigated by the NTSB.